As video becomes a more critical tool in physical security applications, it is important to understand the technology from a transmission standpoint. Video is an extremely useful tool for detecting and investigating incidents. However, if the video quality is not good enough to detect or determine the details of an incident, the system is a poor investment.
The transmission infrastructure is often the cause of quality problems in video, but these problems are preventable with the proper system design and installation. A key to proper system design is a well-designed transmission infrastructure.
Challenges to Transmission
Video signals must be transmitted some distance from cameras to recorders and display monitors, and they must retain the same quality that was developed at the source. This is a major challenge due to a number of common factors.
Bandwidth Limitations. Video is a complex, broad-bandwidth signal in its basic form. Video transmissions contain complex signals whose components are near 0 Hz at the low end of the video frequency spectrum and as high as 10 MHz for highly detailed information. Anything that restricts this bandwidth will affect the image quality. Low-frequency response is as critical as high-frequency response.
Frame Rate. The video signal contains a real-time stream of images running at 60 fields/second (the U.S. standard for live video). In some restricted bandwidth channels, the signal is modified to deliver less than real time. In slow-scan systems this is referred to as refresh rate.
Interference from External Sources. The video signal is susceptible to electrical magnetic interference (EMI). High-frequency interference will affect the detail components of the image, while low-frequency interference, such as power lines, will affect the video signal with rolling noise bars.
Ground Loops. Ground loops are a common problem in video signal transmission. Ground loops occur when different ground potentials exist throughout the infrastructure. They create the same type of visual interference as power lines.
Latency. Latency defines the time it takes the video signal to get from the source to the destination. Many of the transmission methods today cause significant latency, or delay. This becomes a serious problem when an operator is trying to operate a motorized camera (PTZ or dome). It is easy to overshoot the target if the latency is significant.
Security. The video signal may be intercepted or extracted by unauthorized people.
S/N Ratio. An overlooked issue in transporting video is the noise caused by interference or other sources during transmission. Noise from electronic processes, known as white noise, can affect the video image as speckles randomly dispersed over the scene. (Most of us have seen this in home videos with poor lighting.)
Noise mixed into a video signal can have a serious effect on the digitization of the signal for compression. The digitizer cannot distinguish between noise and valid video information and thus tries to compress the noise. The noise makes more work for the digitizer by appearing as picture details.
Cost. The transmission infrastructure is often the most expensive part of the video system. Scrimping in cost on the transmission infrastructure can result in unusable video, creating a system that doesn’t meet the security objectives.
When you budget for a transmission system, consider the following issues:
• Cost of the cable, wire or fiber optics medium. Plenum cable requirements should be considered in this phase of budgeting.
• Cost of the labor to pull the cabling.
• Cost of transmitters and receivers.
• Cost of support equipment such as video switchers, digital amplifiers (DAs) and video (i.e. analog) amplifiers (VAs).
Several transmission media and technologies can be used to transmit analog and digital video, and each deals with the above challenges more or less well.
Analog Video Transmission
Analog, or composite, video is still the most common source today. A J.P. Freeman report claims that new designs are still at least 70% analog cameras. This type of video is called composite video because it combines separate signals, such as vertical-horizontal synchronization and color (red, green and blue), into one using industry-standard encoding such as NTSC. Most existing installations have analog cameras.
Here are the most common methods for transmission of analog video.
In the early days of CCTV, coaxial cable was the most common method of transporting video. There are three common standards of coax: RG-59/U, RG6/U and RG11/U. These cables have a copper core molded into a dielectric material and shielded with a copper braid used as a ground. The common connector used with these coax cable models is the BNC type.
When properly installed, coax cable can transport composite video up to its rated distance. The rated distances for a 10MHz signal are:
• RG-59/U = 441'
• RG-6/U = 789'
• RG-11/U = 1200'
The rating is the length at which the signal drops 3 db in level. Proper installation methods need to be followed to reach these distances. Multiple splices or tight bends in the cable can affect these ratings.
Unfortunately, designers and installers tend to take coax cable farther than its rated length thinking there is little effect. In addition, many installers are not properly trained on the installation of BNC connectors. If improperly installed, the BNC junctions can cause additional loss in signal strength as well as poor shielding. Many coax installations today carry noisy video because of poor installation.
Coax cable loses high frequency as its length is increased. Some manufacturers offer video amplifiers that can amplify the video signal and pre-emphasize its high frequencies, allowing you to extend the length of the cable. This technique, when done properly, can improve the cable length. In these applications, the VA must be installed at the camera end and the equalization must be adjusted using an oscilloscope to optimize the high frequency pre-emphasis.
• Overall, coax is the least expensive solution for transporting video in distances under 2,000 feet.
• Since most cameras (domes and conventional) have BNC outputs, the simplest method is coax.
• Coax doesn’t require a transmitter and receiver as do other techniques.
• Coax is susceptible to EMI and ground loop problems even though it is a shielded cable.
• As pointed out above, it can be installed incorrectly, resulting in numerous problems.
Twisted pair transmission is another popular method for transporting video. It uses a twisted pair of wires instead of coax. The wire is less expensive than coax, but the system requires a transmitter on the source side and a receiver on the receiving side to modify the baseband video to run on the twisted pair. The rated distances are similar to those of coax; however, with heavy enough wire and a bigger power supply, distances up to 4,000 feet are quoted.
• Twisted pair wire is less expensive than coax cable, and with proper equipment and wire size, it can support a video signal at a greater distance.
• Twisted pair is more forgiving in the installation than coax.
• Typical installation uses CAT5 connectors, which are easy to install compared to BNCs.
• The twisted pair system requires a transmitter on the source side and a receiver on the receiving side. This adds cost, often making the complete system more expensive than coax.
Fiber-optic transmission uses glass fibers as the medium instead of copper. The technology converts an electronic signal to light modulation, which travels down the optical fiber. The main two methods used in fiber-optic video transmission are single mode and multi mode, and the distances between them vary. Fiber optics used to require skilled personnel to install the fiber and fiber connectors. Since the cable is glass, splicing or cutting the cable must be done accurately to minimize light loss (signal loss). Most manufacturers today have solved this problem with simple-to-use tools.
• Fiber optics can transmit high-quality video over miles.
• It is immune to normal EMI.
• Fiber optics is more secure than copper. To intercept the signal one must break the glass fiber, which is not an easy task.
• Fiber-optic cable is more expensive than copper, and the connectors are more expensive.
• It also requires the extra cost of transmitters and receivers.
There are other transmission techniques; however, they are usually exceptions. In cases where cable cannot be trenched, for example, microwave or RF techniques can be used. Microwave transmission requires line of sight, which may not always be available. RF is used with directional antennas to limit interference and meet FCC standards. Both methods tend to be expensive and thus are only practical when the standard methods above or below won’t work.
Digital Video Transmission
The newer transmission methods are based on a compressed digital video signal. Analog video can’t be compressed cost effectively. But new ASICs (dedicated LSI chips) and DSP technology have brought down the cost of digitizing and compressing video. Compression is necessary for transporting digital video, since digitization results in a much larger signal than the original analog signal. However, with modern compression algorithms, streaming video is now cost effective. (Streaming video in this article refers to a digitized and compressed video stream.)
Digitization and compression open the door for other transmission methods. Two of the most common of these are telco and IP video.
In the early stages of remote video applications, streaming video was sent via POTS (plain old telephone service), ISDN and T1. POTS, of course, has a very limited bandwidth. When video is sent via POTS, it is usually not real time, and if it is, the image is reduced in size and resolution in order to fit into the POTS bandwidth. ISDN 2B has a 128Kbs bandwidth, so it can accommodate a real-time picture at limited resolution. T1 is 1.5Mbs, which will accommodate full-resolution, real-time video.
• Telco methods offer another option for long-distance transmissions that is cost effective.
• Based on the bandwidth available, telco is a good trade-off in remote applications.
• Low-cost methods such as POTS offer limited quality.
• ISDN and T1 are very expensive.
The new paradigm in video transmission is IP video. IP video is a streaming video that supports TCP/IP protocol. In short, it is network video. IP video connects directly to Ethernet and can be handled as normal network data.
Today we see IP cameras and IP domes; these are cameras that connect directly to the local Ethernet infrastructure. IP video can go anywhere in the world via a LAN/WAN. There are also encoders and decoders available, allowing users of existing analog systems to convert them to IP video.
• IP video offers unlimited distance and can be controlled and viewed from a PDA phone, laptop or other mobile device.
• It can be managed by internal IT departments, saving costly outside maintenance.
• With IP video, adding a camera is simple and cost effective.
• IP video is also available in wireless form using 801.11 standards.
• It is encrypted for security.
• It is cost effective and offers low-cost recording using standard network recorders.
• It eliminates the need for an analog matrix switch, and it offers analytics.
• Open IP video has multiple business applications within the corporation. When the CSO is looking at ROI, it is easy to get other departments to help cost-justify the installation of or conversion to IP video.
• IP video has fewer cons than pros, but many perceived negatives. For example, networks are perceived to be unstable. This is not a valid assumption. The IT industry has developed products that ensure a stable system.
• There is a perception video will overload existing networks. This again is not a valid assumption. There are products and algorithms that reduce the network load.
• There is a perception that streaming video is of lower quality than analog. This argument is partially true. However, the latest algorithms offer high-quality video in a relatively narrow bandwidth.
• The major downside of IP video is the lack of awareness in our industry of its value and how to implement it.
The video transmission infrastructure is critical to the total cost and performance of a video system. The CSO should understand the downsides and quality implications of a substandard infrastructure.
Ray Payne has 25 years of experience in senior management for major physical security manufacturers. He has been responsible for product development and product management teams at several companies, and he introduced many firsts in CCTV and IP video products applied to physical security applications.